Method of solvent extraction



United States Patent Ofiiice 3,125,410 METHOD OF SULVENT EXTRAQTIONNathan E. Ballou, 1531 Campus Drive, Berkeley 8, Calif., and Edith M.Scadden, 2637 Clay St, San Francisco, (Iali- The invention describedherein may be manufactured and used by or for the Government of theUnited States of America for governmental purposes Without the paymentof any royalties thereon or therefor.

This invention relates to a method for extracting elements from aqueoussolutions thereof and more particularly to an extraction process using aselective organic solvent.

This is a division of a patent application, Serial #437,893, nowabandoned, filed in the U8. Patent Otlice by the same inventors, June18, 1954, and entitled Method of Solvent Extraction.

One object of this invention is to provide a method of separatingcertain elements from most all other elements.

Another object is to provide a method of separating these certainelements from each other.

Still another object is to provide an extraction method suitable forseparating either macro or trace concentrations of the elements.

Other objects are to provide a solvent separation method capable ofbenig conducted at room temperature under ordinary laboratoryconditions, and which Will he more efiicient, quicker, and economical.

These and other objects will become apparent from the following detaileddescription:

According to this invention it has ben found that the elements of groupsIVA, VA, tin, yttrium, protactinium, thorium, indium and the heavy rareearth elements of the type 4f (atomic numbers 65 through 71) and type 5f(atomic numbers 97 and above) of Hubbards Periodic Chart of the Atoms(revised edition, 1950), published by W. M. Welch Scientific Co.,Chicago, can be extracted from aqueous acid solutions thereof by the useof alkyl phosphates, in more particular, the invention provides a methodof extracting the elements of group IVA, thorium and indium from otherelements including the elements of group VA.

The acids used to produce the aqueous solutions must be of such acharacter as will not preferentially complex, at the concentrations atwhich they are present in the solution, the particular elements underconsideration in contrast to the complexing of the elements with thealkyl phosphate. These acids are designated with reference to theelements in question as non-complexing acids. The

solutions can be made with one non-complexing acid alone or withmixtures of two or more.

Conveniently this process is carried on with acid conoentrations in theaqueous phase 'of the order of at least about one molar (1 M). Sincecertain acids such as hydrofluoric, oxalic, malic, tartaric, citric andlactic are known to complex the elements in question, their use shouldbe avoided or their concentrations held to certain limited ranges wherethey do not complex objectionably, these ranges depending on theconcentration of other acids in the aqueous phase and on theconcentration of the alkyl phosphate. For example, when the aqueousphase is one M in sulphuric acid and the alkyl phosphate used is 0.06 Mdi-n-butyl phosphoric acid, oxalic acid in a concentration as high as0.004 M is not objection-able.

Alkyl phosphates, in-general, can be used as the extractive agent, beingemployed in what is designated as the organic phase. Alkyl phosphatesreadily available 3,125,410 Patented Mar. 17, 1964 commercially includethe mono, di and tri-alkyl esters of phosphoric acid. Single alkylphosphates can be used or mixtures of two or more. For example, therehas been found to be quite satisfactory for use with this invention,mixtures of di-n-butyl phosphoric acid and mono-n-butyl phosphoric acid,sometimes referred to as 'di-n-butyl hydrogen phosphate, andmono-n-butyl dihydrogeu phosphate, respectively, derived from thecommercially available normal butyl phosphoric acid.

While the alkyl phosphate extracting agent can, under somecircumstances, be used in its pure form, it is usually, as a practicalmatter, dissolved in an organic solvent which is immiscible with theaqueous phase. Generally, any known organic solvent for the alkylphosphates is suitable including ethers, hydrocarbons, and halogenatedhydrocarbons. Di-n-butyl ether was used in the following examplesbecause its boiling point falls in a region convenient for experimentalpurposes.

The method involves intimately mixing the aqueous solution with theorganic phase, and thereafter separating the phases either by allowingthe phases to separate by flotation or to expedite the separation, bycentrifuging. The mixing can be accomplished by stirring, shaking orusing countercurrent solvent extraction apparatus or other suitablemeans. The following examples are illustrative.

Example I Aqueous phases, one M in nitric acid, containing carrier-free(i.e. trace) concentrations of elements of groups IVA, VA, indium, tin,thorium, protactinium, yttrium and the heavy rare earth elements of thetypes 4f and 5f were intimately mixed fora period of five minutes withorganic phases made by dissolving mixed normal butyl phosphoric acids indi-normal butyl ether to a concentration of 0.6 M di-n-butyl phosphoricacid and 0.13 M mono-n-butyl phosphoric acid. The volume ratio oforganic to aqueous phases was one to one. After mixing, thetwo phaseswere separated by centrifugation. The organic phase was found to haveextracted at least about 85% of the above mentioned elements in thisexample. The primary extracting agent in this example is the di-nbutylphosphoric acid, whereas, the mono-n-butyl acid has a secondaryextracting effect, being not as powerful an. extractive agent as thedi-n-butyl phosphoric acid.

Example 2 V Aqueous phases, one Min sulphuric acid, and 0.004 M inoxalic acid, containing macro concentrations of the elements of groupsIVA, VA, indium, thorium, protactinium, yttrium, tin and the heavy rareearth elements of types 4f and 5f were intimately mixed for a period of5 minutes With organic phases made by dissolving mixed n-butylphosphoric acids in di-n-butyl ether to a concentration of 0.6 Mdi-n-butyl phosphoric acid and 0.13 M mono-n-butyl phosphoric acid. Thevolume ratio of organic to aqueous phases was one to one. After mixing,the two phases were separated by centrifugation. The organic phase wasfound to have extracted at least about of the above mentioned elementsin this example except for tin which extracted to the extent of at least50%. The presence of 0.004 M oxalic acid, one of the agents known tocomplex elements of this category, did not have any deleteriouspreferential complexing eifect. The primary extracting agent in thisexample is the di-ubutyl phosphoric acid. The mono-n-butyl phosphoricacid has a similar secondary effect as noted under Example 1.

To facilitate separation of group IVA, indium and thorium from group VAand protactinium, advantage can be taken of the change in complexingability of the alkyl phosphate with its concentration as shown in thetwo following examples.

Example 3 Aqueous phases, one M in nitric acid, containing carrier-freeconcentrations of the elements of groups IVA, VA, indium, thorium andprotactinium were intimately mixed for a period of 5 minutes withorganic phases made by dissolving di-n-butyl phosphoric acid indi-n-butyl ether to a concentration of 0.06 M. The volume ratio oforganic to aqueous phases was one to one. After mixing, the two phaseswere separated by centrifugation. The organic phase was found to haveextracted at least about 95% of the elements of the group IVA, thorium,and indium, and less than 5% of the elements of group VA andproactinium.

Using, in place of di-n-butyl phosphoric acid alone, a mixture ofdi-n-butyl phosphoric acid and mono-n-butyl phosphoric acid at aconcentration of 0.06 M di-n-butyl phosphoric acid and a one M ratio ofthe dito mono n-butyl phosphoric acids of 4.5 to 1, substantially thesame amount of the category consisting of group IVA, thorium, and indiumwere extracted in a 5 minute mixing period as with the di-n-butylphosphoric acid alone, but 5 to of the category consisting of group VAand protactinium were also extracted in a 5 minute mixing period. Byreducing the mixing period, to say 2 minutes, the amount of group IVA,thorium, and indium extracted remains substantially the same but theextraction of group VA and protactinium is reduced to less than 5%.

Example 4 Aqueous phases, one M in sulphuric acid, containing macroconcentrations of the elements of groups IVA, VA, indium, thorium, andprotactinium were intimately mixed for a period of minutes with organicphases made by dissolving di-n-butyl phosphoric acid in di-n-butyl etherto a concentration of 0.06 M. The volume ratio of organic to aqueousphases was one to one. After mixing, the two phases were separated bycentrifugation. The organic phase was found to have extracted at leastabout 95% of the elements of group IVA and thorium, 85% of the indium,and less than 5% of the elements in group VA and protactinium.

While Example 2 indicated that at least 80% of the elements of group VAwere extracted, there is in fact an appreciable spread above thisminimum between the percentages of niobium and tantalum extracted. Thisspread can be used to advantage for the enrichment of a tantalum orniobium fraction, as shown in the following example.

Example 5 Aqueous phases, 2 M in sulphuric acid, containing macroconcentrations of tantalum and niobium were intimately mixed for aperiod of 5 minutes with organic phases made by dissolving di-n-butylphosphoric acid in di-n-butyl ether to a concentration of 0.15 M. Thevolume ratio of organic to aqueous phases was one to one. After mixing,the two phases were separated by centrifugation and the organic phasewas found to have extracted about 65% of the tantalum and about of theniobium. The amount of spread has been found to be a function of boththe concentration of the di-n-butyl phosphoric acid and the acid in theaqueous phase.

When the extraction of elements is undertaken by the use of alkylphosphate according to the present invention, it is sometimes desirableto prevent or inhibit the extraction of the elements in the categoryconsisting of group VA and protactinium. This is the case, for example,when it is desired to separate elements of group VA and protactiniumfrom others extractable by alkyl phosphates. This inhibiting can beaccomplished, as evident from the preceding examples, by using lowconcentrations of alkyl phosphate or by shortening the period of contactbetween the aqueous and organic phases. Also contemplated is the use ofhydrogen peroxide as an inhibitor for the elements in group VA andprotactinium, as shown in the following exarnple.

Example 6 With niobium, as representative of the category consisting ofthe elements of group VA and protactinium, in carrier-freeconcentrations in a one M nitric acid aqueous phase, an organic phase of0.5 M di-n-butyl phosphoric acid and 0.47 mono-n-butyl phosphoric indi-n-butyl ether, with a ratio of the organic phase to the aqueous phaseof one to one, and a mixing time of 5 minutes, extracted over 96% of theniobium. When the example experiment was repeated with hydrogen peroxidepresent in the aqueous phase at a concentration of 3% by Weight of theaqueous phase there resulted an extraction of about 67% of niobiumduring the same 5 minute mixing time. With the same hydrogen peroxidepercentage, if the mono-n-phosphoric acid is reduced to 0.003 M theextraction of niobium is reduced to 21%.

While the foregoing examples illustrate the process carried on with asingle extraction, it is apparent that more of the elements underconsideration can be extracted by repeated extractions with freshbatches of alkyl phosphate.

According to the invention there is afforded a simple and expedientprocess for extracting selectively certain elements from aqeoussolutions to separate them from most other elements. The process can beconducted under ordinary laboratory conditions and obviates manydisadvantages present in other known methods; for example, no specialapparatus is required, nor must the experiments be conducted underextremely precise and critical conditions. Furthermore, separations bythis invention have been found to be considerably more economical.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

We claim:

1. A method of extracting elements of group IV-A, indium and thoriumfrom an aqueous solution formed with nitric acid having an aqueous phaseof about one M, said solution including elements of both groups IVA andVA and protactinium, comprising intimately mixing said aqueous solutionwith a substantially equal volume of organic solution includingdi-n-butyl phosphoric acid in a concentration of about 0.06 M, saidorganic solution being immiscible with said aqueous solution and beingotherwise physically and chemically compatible with the desiredextraction, and said organic solution being formed by dissolving amixture of di-n-butyl phosphoric and mono-nbutyl phosphoric acid (bothin their pure form) in all organic solvent to a concentration of 0.06di-n-butyl phosphoric acid and a one M ratio of di-to-mono-n-butylphosphoric acids of 4.5 to 1.

2. The method of claim 1 wherein said mixing period is limited to abouttwo minutes.

References Cited in the file of this patent UNITED STATES PATENTS2,683,655 Peppard July 13, 1954 2,789,878 Peppard Apr. 23, 19572,796,320 Spedding June 18, 1957 2,824,783 Peppard et al Feb. 25, 19582,882,124 Seaborg Apr, 14, 1959 2,883,264 Warf Apr. 21, 1959 OTHERREFERENCES AEC Document AECD 2524, declassified March 11, 1949.

Scadden et al.: Anal. Chem, volume 25, No. 11, pages 16024604, November1953.

AECD Document DP 250, pages 4-22.

1. A METHOD OF EXTRACTING ELEMENTS OF GROUP IV-A, INDIUM AND THORIUMFROM AN AQUEOUS SOLUTION FORMED WITH NITRIC ACID HAVING AN AQUEOUS PHASEOF ABOUT ONE M, SAID SOLUTION INCLUDING ELEMENTS OF BOTH GROUPS IVA ANDVA AND PROTACTINIUM, COMNPRISING INTIMATELY MIXING SAID AQUEOUS SOLUTIONWITH A SUBSTANTIALLY EQUAL VOLUME OF ORGANIC SOLUTION INCLUDINGDI-N-BUTYL PHOSPHORIC ACID IN A CONCENTRATION OF ABOUT 0.06 M, SAIDORGANIC SOLUTION BEING IMMISCIBLE WITH SAID AQUEOUS SOLUTION AND BEINGOTHERWISE PHYSICALLY AND CHEMICALLY COMPATIBLE WITH THE DESIREDEXTRACTION, AND SAID ORGANIC SOLUTION BEING FORMED BY DISSOLVING AMIXTURE OF DI-N-BUTYL PHOSPHORIC AND MONO-NBUTYL PHOSPHORIC ACID (BOTHIN THEIR PURE FORM) IN AN ORGANIC SOLVENT TO A CONCENTRATION OF 0.06DI-N-BUTYL PHOSPHORIC ACID AND A ONE M RATIO OF DI-TO-MONO-N-BUTYLPHOSPHORIC ACIDS OF 4.5 TO 1.